Tag: Geology

We always seem to be “overdue” a devastating asteroid impact, but how can we be overdue if asteroids don’t have an impact schedule?

Don Davis/NASA

Humans are naturally tuned to seek out patterns in seemingly random events. It’s an evolutionary trait that has helped us become the smart Homo sapiens we are today.

This ability to spot patterns and predict cyclical events continues to dominate our everyday lives. For example, geologists chart seismic activity in hopes of seeing a tell-tail earthquake signal before the “big one” happens; farmers track seasonal cycles in an attempt to predict periods of drought; Wall Street traders use complex numerical models to warn of the next financial crisis (or, indeed, profit from the downturn). Also, astronomers try to find patterns in cosmic occurrences that could pose an existential threat.

We are, of course, talking asteroid impacts — cataclysmic events that have shaped all of the planets in our solar system. Although Earth’s atmosphere is very good at eroding away ancient impact craters, evidence for asteroid impacts in the geological history of our planet is very common. Frankly, it’s perfectly natural to be hit by large asteroids and comets; that’s how planets accrete rocky material, collect water and accumulate organic chemistry for life (on Earth, at least).

But should we get hit by a massive asteroid in the near future, it could be curtains for our civilization. So it sure would be handy if we could somehow use the geologic record of our planet, see how often we get punched, spot a cycle or some kind of pattern, predict then the next impact is likely to happen and — hopefully — plan for the next marauding space rock to make an appearance in our skies! (Whether we’ll be able to do anything about it is an entirely different matter.)

But what could drive periodic asteroid or comet impacts in the first place? One hypothesis claims that the solar system’s “wobble” through the galactic plane may destabilize comets in the Oort Cloud periodically, causing an uptick in massive planetary impacts. Also, the much hyped solar twin, Nemesis, could gravitationally jumble asteroids during its long orbit around the sun. But neither hypothesis stands up to scrutiny and the existence of an extremely dim solar partner is becoming increasingly unlikely.

Regardless, previous studies have suggested that extinction-level impacts (of the magnitude of the one that wiped out, or at least greatly contributed to the extinction of the dinosaurs) occur roughly every 26 million years (the cause of which is open to debate), but researchers from ETH Zurich and Lund University in Sweden now refute this claim.

“We have determined … that asteroids don’t hit the Earth at periodic intervals,” Matthias Meier, of ETH Zurich’s Institute of Geochemistry and Petrology, said in a statement.

After studying precisely-dated impact craters around the world that were formed in the past 500 million years, Meier and Sanna Holm-Alwmark of Lund University dated some 22 craters with dates of impacts known to a precision of one percent.

Then, using a technique known as circular spectral analysis (CSA), they attempted to find the approximate-26 million year period in this set of craters. They found no such period.

Interestingly, Meier and Holm-Alwmark also found that some of the impact craters were of the same age, hinting at a common source. “Some of these craters could have been formed by the collision of an asteroid accompanied by a moon,” said Meier. “But in other cases, the impact sites are too far away from each other for this to be the explanation.”

One interesting example is the apparent close similarity in age of the famous 66 million-year-old, 110 mile-wide Chicxulub Crater in Mexico (that has been linked with the extinction of the dinosaurs) and the 15 mile-wide Boltysh Crater in the Ukraine. As pointed out by the researchers, although a definitive explanation for this coincidence isn’t immediately clear, the two impactors may have originated from a collision in the asteroid belt, sending fragments to Earth, hitting the planet within a very short period of one another.

And it’s these kinds of clustering impacts that the researchers have identified as being potential problems with previous statistical studies — they assumed each impact is distinct, when in fact, they happened at the same time, possibly skewing results and creating a pattern when, in fact, there wasn’t one.

“Our work has shown that just a few of these so-called impact clusters are enough to suggest a semblance of periodicity,” said Meier.

I have little doubt that these new findings will be disputed, spawning more studies pointing to other statistical techniques and a bigger impact crater data set, but it is interesting to think that, as far as extinction-level impact events go, there really may be no pattern to their occurrence.

We know that a doomsday asteroid is out there, and it will hit us, but it has a random impact date that is only known to our planet’s geological future.

Around 3.5 billion years ago — when basic life was just gaining a foothold on Earth — the Tharsis region on Mars was swamped with vast floods that scar the landscape to this day.

Mars wears its geological history like a badge of honor — ancient craters remain unchanged for hundreds of millions of years and long-extinct volcanoes look as if they were venting only yesterday. This is the nature of Mars’ thin, cold atmosphere; erosional processes that rapidly delete Earth’s geological history are largely absent on the Red Planet, creating a smorgasbord of features that provide planetary scientists with an open book on Mars’ ancient past.

In this latest observation from the European Mars Express mission, a flood of biblical proportions has been captured in all its glory. But this flood didn’t happen recently, this flood engulfed a vast plain to the north of the famous Valles Marineris region billions of years ago.

It is believed that a series of volcanic eruptions and tectonic upheavals in the Tharsis region caused several massive groundwater releases from Echus Chasma, a collection of valleys some 100 kilometers (62 miles) long and up to 4 kilometers (2.5 miles) deep. These powerful bursts of water carved vast outflow channels into the adjacent Lunae Planum, contributing to the formation of the Kasei Valles outflow channels, releasing water into the vast Chryse Planitia plains which acted as a “sink.” Smaller “dendritic” channels can be seen throughout the plain, indicating that there were likely many episodic bursts of water flooding the region.

In the middle of what was likely a powerful, vast and turbulent flows of water is Worcester Crater that was created before the Tharsis floods and, though its crater rim stands to this day and retains its shape, it was obviously affected by the flow of water, with a “tail” of sediment downstream.

ESA Mars Express observation of the mouth of Kasei Valles, as it transitions into Chryse Planitia. The large crater in the lower left is Worcester Crater (ESA/DLR/FU Berlin)

Also of note are smaller “fresh” craters that would have appeared long after the flooding took place, excavating the otherwise smooth outflow channels. These younger craters have tails that seem to be pointed in the opposite direction of the flow of water. These tails weren’t caused by the flow of water, but by the prevailing wind direction.

From orbital observations by our armada of Mars missions, it is well known that these channels contain clays and other minerals associated with the long-term presence of water. Although the Red Planet is now a very dry place, as these beautiful Mars Express images show, this certainly hasn’t always been the case.

The laser-zapped rock “Coronation” — inset image was taken by the ChemCam instrument, featuring the small laser burn. Credit: NASA/JPL-Caltech

After Mars rover Curiosity’s thunderous landing on Aug. 5/6, any hypothetical Martian on the surface would have been forgiven for being a little confused.

Setting down on the flat plain called Aeolis Palus inside Gale Crater, the six-wheeled, one-ton, nuclear-powered rover would have looked more like an alien battle tank being dropped off by a rather ominous-looking “Flying Saucer” than a scientific mission. But after the famous “sky crane” maneuver that lowered the rover with the precision of a Harrier Jump Jet, the “alien” robot didn’t start rolling over the Martian landscape zapping Mars rocks with its laser. Instead, it just sat there. For days. Occasionally there’d be a bit of action — such as Curiosity’s cameras swiveling, mast raising and high-gain antenna tracking the sky — but apart from that, our hypothetical Martians would probably not have thought much of this lack-luster invasion by an airdropped tank.

But that all changed today. Curiosity blasted a rock with its laser, marking the beginning of Curiosity’s Mars domination! Shock and awe, Mars rover style.

Alas, this isn’t a military exercise, but it is significant. Today marks the first day that one of our interplanetary robotic emissaries have used a laser on another planet in the name of science. NASA mission operators gave the go-ahead to carry out a test-run of the Chemistry and Camera instrument, or ChemCam, targeting a small rock (called “Coronation”) with 30 pulses of its laser over a 10-second period. According to the JPL press release, each pulse delivered more than a million watts of power for about five one-billionths of a second.

The fist-sized Mars rock — called “Coronation”, previously designated “N165” — has become the first casualty of war scientific target of Curiosity’s ChemCam instrument. Credit: NASA/JPL-Caltech

“We got a great spectrum of Coronation — lots of signal,” said ChemCam Principal Investigator Roger Wiens of Los Alamos National Laboratory, N.M. “Our team is both thrilled and working hard, looking at the results. After eight years building the instrument, it’s payoff time!”

The laser works by vaporizing the surface layers of exposed rock. Under the intense heating by such focused energy, a tiny sample of material rapidly turns into plasma. The the flash of light generated by the small, rapidly dissipating cloud of plasma can then by analyzed from afar by the ChemCam’s spectrometer. The light reveals what kinds of elements are contained in the sample, aiding Curiosity’s studies of the Red Planet. And the best thing is that ChemCam appears to be working better than expected.

“It’s surprising that the data are even better than we ever had during tests on Earth, in signal-to-noise ratio,” said ChemCam Deputy Project Scientist Sylvestre Maurice of the Institut de Recherche en Astrophysique et Planetologie (IRAP) in Toulouse, France. “It’s so rich, we can expect great science from investigating what might be thousands of targets with ChemCam in the next two years.”

Rocks and regolith strewn over the ground near Mars rover Curiosity. Credit: NASA/JPL-Caltech

It looks like rocks and dust, right? Actually, it resembles the dusty parking lot near a beach where my family used to holiday when I was young — a sandy, ruddy, dusty patch devoid of grass where cars had worn down the top layer of dirt, exposing smoothed rock underneath. However, this isn’t a parking lot. Actually, scrub that, it IS a parking lot — Mars rover Curiosity’s parking lot in Aeolis Palus, a remarkably smooth plain inside Gale Crater on Mars.

As Curiosity undergoes a software upgrade preparing it for surface operations, we’ve been patiently waiting for the mission site to upload new images (beyond the color thumbnail teasers) of the surrounding area. And it seems that on Saturday night that happened. Here are some of my favorite views from Curiosity’s Mastcam:

Curiosity’s sundial on its deck reads: “Mars 2012 — To Mars To Explore”Discoloration in the top soil in the location of a crater formed by Curiosity’s Sky Crane rockets. Credit: NASA/JPL-CaltechThe deployed high-gain antenna. Credit: NASA/JPL-CaltechThe crater rim and detail of undulating terrain — possibly dunes. Credit: NASA/JPL-Caltech